Biometrical Letters Vol. 50(2), 2013, pp. 61-80
|
A BAYESIAN MODEL TO COMPARE VINIFICATION PROCEDURES
Federico Mattia Stefanini1, Ottorino-Luca Pantani2 1Dipartimento di Statistica, Informatica, Applicazioni 'G.Parenti', Università degli Studi di Firenze, viale Morgagni 59, I-50134 Firenze, Italia, e-mail: stefanini@disia.unifi.it 2Dipartimento di Scienze delle Produzioni Agroalimentari e dell'Ambiente, Università degli Studi di Firenze, Piazzale Cascine 28, I-50144 Firenze, Italia, e-mail: OLPantani@unifi.it |
The effects of three pre-fermentative techniques (standard procedure, cold soak pre-fermentation and cryomaceration), temperature (20 or 30°C) and saignée (with/without) on the extraction of total anthocyanins were investigated during maceration of must obtained from Sangiovese grapes. A Bayesian hierarchical model was developed to estimate time-dependent contrasts while addressing the peculiar features displayed by the experimental units (wine tanks): substantial heterogeneity among replicates, departure from low-order 'textbook' kinetics and the occasional presence of very low observations. Prior distributions of critical model parameters were elicited with the help of wine-making experts and by considering the results of previous experiments. The posterior distribution of model parameters was approximated by Markov Chain Monte Carlo simulation using JAGS software. Among the main findings, it is to be highlighted that temperature and saignée increased the total anthocyanin concentration in all the techniques, although at different times during maceration. In all the procedures the total anthocyanin gain decreased as the maceration came to an end.
semiparametric regression, outliers, MCMC, wine making, pre-fermentation treatments
